The invention relates to a coal or biomass medium low temperature pyrolysis quality improving system and a method for producing quality improved coal, high calorific value pyrolysis gas and tar or liquefied synthetic oil by utilizing the system. By utilizing the system and the method, effective capture of carbon dioxide can be realized. The system comprises a medium low temperature pyrolyzing furnace in a moving bed type preferably, at least one catalysis-heat carrier-oxygen transfer material regenerator communicated with the medium low temperature pyrolyzing furnace, a solid-solid separator and a condenser. In the medium low temperature pyrolyzing furnace, raw coal is subject to medium low temperature pyrolysis, and the quality improved coal, the high calorific value pyrolysis gas and the tar or liquefied synthetic oil gas are produced, wherein the tar or liquefied synthetic oil gas is condensed into jar or liquefied synthetic oil; and in the catalysis-heat carrier-oxygen transfer material regenerator, a saturated waste catalysis-heat carrier-oxygen transfer material is regenerated by oxidation and enters into the medium low temperature pyrolyzing furnace again, thus realizing regenerating cycle of catalysis-heat carrier-oxygen transfer materials.